System for performing bonding a first substrate to a second substrate

ABSTRACT

A system for performing bonding of a first substrate including a first plurality of solder pads to a second substrate including a second plurality of solder pads comprises a first alignment mark set and a first plurality of dots on the first substrate. The system further comprises a second alignment mark set and a second plurality of dots on the second substrate. The second plurality of dots are configured to interlock and form an interlocking key with the first plurality of dots. The first alignment mark set is aligned with the second alignment mark set corresponding to the first and second plurality of dots being aligned and the first and second plurality of solder pads being aligned. The first and second plurality of dots are configured to remain substantially solid during a reflow of the first plurality of solder pads.

BACKGROUND

In fabricating disk drives, such as energy assisted magnetic recording(EAMR) disk drives, it may be necessary to bond substrates. For example,in conventional EAMR disk drives, a laser provides energy used to heatthe media for magnetic recording. The laser typically takes the form ofa laser diode. The laser diode may be desired to be bonded with theslider.

FIG. 1 depicts a conventional method 10 for bonding two substrates, suchas a conventional laser diode (or substrate on which the laser dioderesides) and a slider. FIGS. 2-3 depict a conventional EAMR head 50during fabrication using the conventional method 10. Thus, twoconventional substrates, a slider 60 and a laser diode 70 are shown.Each conventional substrate 60 and 70 includes conventional alignmentmarks 62 and 72, respectively. Each conventional substrate 60 and 70also includes conventional solder pads 64 and 74, respectively. Theconventional substrates 60 and 70 are aligned, via step 12. Typicallythis is accomplished by aligning the alignment marks 62 on one substrate60 with the alignment marks 72 on the other substrate 72. FIG. 2 depictsthe conventional substrates 60 and 70 after step 12. Thus, the alignmentmarks 62 and 72 and solder pads 64 and 74 are aligned.

Once alignment has been achieved, the substrates 60 and 70 are heated toreflow the solder 64 and 74. FIG. 3 depicts the conventional substrates60 and 70 after step 14 is performed. Mechanical and electricalconnection is made between the substrates 60 and 70 by pads 64′/74′,which have been reflowed together.

Although the conventional method 10 may function, the alignment achievedafter the reflow step 14 may be limited. For example, after the method10 is completed, the post-bonding alignment accuracy may be on the orderof greater than one micron. For example, as can be seen by comparingFIGS. 2 and 3, the substrates 60 and 70 have moved with respect to eachother after the reflow. In applications, such as EAMR heads 50, greateralignment accuracy is desired.

Accordingly, what is needed are improved methods and systems for bondingsubstrates, for example in bonding substrates used in EAMR disk drives.

BRIEF SUMMARY OF THE INVENTION

A method and system for performing bonding of a first substrate to asecond substrate are described. The first substrate includes a firstplurality of solder pads and a first alignment mark set. The secondsubstrate includes a second plurality of solder pads and a secondalignment mark set. The method and system include aligning the firstalignment mark set on the first substrate to the second alignment markset on the second substrate. The first substrate includes a firstplurality of dots. The second substrate includes a second plurality ofdots configured to interlock with the first plurality of dots. The firstalignment mark set being aligned with the second alignment mark setcorresponds to the first plurality of dots being aligned with the secondplurality of dots and the first plurality of solder pads being alignedwith the second plurality of solder pads. The method and system alsoinclude locking the first plurality of dots with the second plurality ofdots to form an interlocking key. In addition, the method and systeminclude reflowing at least one of the first plurality of solder pads andthe second plurality of solder pads. The first plurality of dots and thesecond plurality of dots remain substantially solid during the reflowingstep.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart depicting a conventional method for bonding aconventional laser diode and a conventional slider.

FIGS. 2-3 are diagrams depicting the conventional laser diode and sliderduring bonding.

FIG. 4 is a flow chart depicting an exemplary embodiment of a method forbonding substrates, for example in fabrication of an EAMR head.

FIG. 5 is a plan view depicting an exemplary embodiment of substrates tobe bonded.

FIG. 6 is a side view of portions of the exemplary embodiment ofsubstrates to be bonded after alignment.

FIG. 7 is a plan view depicting an exemplary embodiment of substrates tobe bonded after alignment and locking.

FIG. 8 is a side view of portions of the exemplary embodiment ofsubstrates to be bonded after alignment and locking.

FIGS. 9-10 depict exemplary embodiments of alignment marks that may beused in aligning substrates.

FIGS. 11-18 are diagrams depicting exemplary embodiments of dots formingan interlocking key for bonding substrates.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 4 is a flow chart depicting an exemplary embodiment of a method 100for bonding substrates, for example in fabrication of an EAMR head.FIGS. 5-8 are diagrams depicting side and plan views of an EAMR head 120during fabrication. For clarity, FIGS. 5-8 are not to scale. Further,for simplicity, not all components are labeled in FIGS. 5-8. Referringto FIGS. 4-8, the method 100 is described in the context of substratesused in fabricating the EAMR head 120. However, the method 100 may beused to form another device (not shown). The EAMR head 120 beingfabricated may be part of a merged head that also includes a readtransducer (not shown in FIGS. 5-8) and resides on a slider of a diskdrive.

FIG. 5 depicts the substrates 130 and 140 for the EAMR head 120 beforethe method 100 commences. For simplicity, only portions of thecomponents on the substrates 130 and 140 are shown. In the embodimentshown, the substrate 130 is the slider while the substrate 140corresponds to the laser. In some embodiments, the substrate 140 may bea laser diode, while in other embodiments, the substrate 140 may be acomponent on which the laser diode is mounted. However, in otherembodiments, the substrates 130 and 140 may correspond to othercomponents. In addition, devices other than an EAMR head 120 may befabricated. The substrate 130 includes solder pads 132 and an alignmentmark set 134. In the embodiment shown, the solder pads 132 include anunder bump metal (UBM) and solder. The UBM typically includes anadhesion layer and a barrier layer. In some embodiments, the adhesionlayer may be a material including Cr, Ti, and/or Ta. The barrier layerresides between the solder and the adhesion layer so that the adhesionlayer is not dissolved into the solder. The barrier layer may includematerials such as one or more of Pt, Ni, W, and Nb. The solder may below temperature solder. However, in other embodiments, the solder pads132 may be formed of different materials. Each mark in the alignmentmark set 134 is in the form of a plus sign. Further, in the embodimentshown, each mark in the alignment mark set 134 is a female. The femalealignment marks 134 are shown in black. The substrate 140 includessolder pads 142 and an alignment mark set 144. In the embodiment shown,the solder pads 142 include UBM and solder. In some embodiments, the UBMmay have a structure analogous to that described above for the substrate130. However, in other embodiments, the solder pads 142 may be formed ofdifferent materials. Each mark in the alignment mark set 144 is in theform of a plus sign, or cross. Further, in the embodiment shown, eachmark in the alignment mark set 144 is a male. The male alignment marks144 are shown as cross-hatched. However, in other embodiments, the malealignment mark set 144 could be on the first substrate 130 and thefemale alignment mark set 134 could be on the second substrate 140.

The first substrate 130 includes a first set of dots 136. Similarly, thesecond substrate 140 includes a second set of dots 146. The dots 136 and146 are configured to interlock, forming an interlocking key during thebonding process. The dots 136 and/or 146 may be made of a materialincluding at least one of Au, Cu, Ni, and NiFe. Although shown as havingcircular cross sections, the dots 136 and/or 146 may have another crosssection. For example, the dots 136 and/or 146 may have a substantiallyrectangular cross-section, and/or a re-entrant cross-section. Inaddition, all of the dots 136 and 146 need not have the samecross-section. Although shown as cylindrical in shape, the dots 136and/or 146 may have another shape. For example, one or more of the dots136 and 146 may have a tapered top. Finally, a particular arrangement ofthe solder pads 132/142, the alignment mark sets 134/144, and/or thedots 136/146 could differ in other embodiments.

The substrates 130 and 140 are aligned, via step 102. Step 102 isperformed by the first alignment mark set 134 on the first substrate 130to the second alignment mark set 144 on the second substrate 140. Insome embodiments, step 102 includes aligning the substrates 130 and 140to within a desired tolerance. In some embodiments, the desiredtolerance is not more than one micron. In some such embodiments, thetolerance is not more than 0.5 micron. By aligning the alignment marksets 134 and 144, the bond pads 132/142 and the dots 136/146 arealigned. FIG. 6 depicts a side view of a portion of the EAMR head 120after step 102 is performed. Thus, the solder pads 132 and 142 arealigned. In addition, the dot 146 on the substrate 140 is aligned with agap between the dots 136.

The first set of dots 136 is locked with the second set of dots 146 toform an interlocking key, via step 104. Step 104 may include applyingpressure to one or both of the substrates 130 and 140. FIGS. 7-8 depictplan and sides views of the head 120 during fabrication. Thus,interlocking key 148 has been formed by the dots 136 and 146. In theembodiment shown, the dots 136 and 146 are not collinear. However, inother embodiments, the dots 136 and/or 146 may be collinear as long asthey form an interlocking key that restricts the relative movement ofthe substrates 130 and 140. The dots 136 are also shown as having thesame cross-sectional shape and a different size than the dots 146. Inother embodiments, the dots 136 and 146 may have different shapes and/orhave the same cross-sectional size. The alignment marks 134 and 144 alsofit together. More specifically, the male alignment mark 144 fits withinthe female 134.

A solder reflow is performed, via step 106. In some embodiments, step106 includes exposing at least a portion of the substrate(s) 130 and 140to heat. In some embodiments, one pad 132 or 142 remains solid, whilethe other pad 142 or 132, respectively, becomes liquid during the reflowstep 106. However, in other embodiments, both pads 132 and 142 maybecome liquid during the reflow step 106. During the reflow step thedots 136 and/or 146 remain substantially solid. As a result, the dots140 and 130 remain locked within a desired tolerance during the reflowstep. In some embodiments, the dots 130 and 140 remain within thetolerances with which they were aligned.

Using the method 100, the bonding of substrates, such as in the EAMRhead 120 may be improved. The interlocking key 148 is formed by the dots136 and 146. The interlocking key 148 confines the relative motion ofthe substrates 130 and 140. Because the dots 136 and 146/interlockingkey 148 remain solid during the reflow step, the alignment between thesubstrates 130 and 140 is substantially preserved during the reflow ofstep 106. Despite at least some portion of the solder pads 132/142becoming liquid during the reflow step, the alignment achieved in step102 may be substantially unchanged. In some embodiments, the substrates130 and 140 remain aligned to within one micron throughout the process100. In some such embodiments, the substrates 130 and 140 remain alignedto not more than 0.5 micron throughout the reflow. Consequently,alignment throughout the bonding process may be improved.

Further, the locking step 104 may improve the mechanical stability ofthe bonding. In some embodiments, the locking step 104 may actually forma joint between the dots 136 and 146. For example, when clean, two goldsurfaces which rub together may form a gold bond. If at least someportion of the dots 136 and some portion of the dots 146 are gold,pressing the substrates 130 and 140 together to form interlocking key148 may cause the bumps 136 and 146 to rub together. Those dots 136 and146 that are gold may be pressed together with sufficient shear force toform a gold bond. Thus, in addition to interlocking because of thegeometry of the patterns of the dots 136 and 146, the key 148 mayactually interlock due to gold bonds. Consequently, the alignmentbetween the substrates 130 and 140 may be better preserved.

Other configurations are possible in addition to those described above.For example, FIGS. 9-10 depict exemplary embodiments of alignment marksets 134′/144′ and 134″/144″ that may be used in aligning substrates 160and 170. For clarity FIGS. 9-10 are not to scale. For example, FIG. 9depicts an alignment mark set in which a cross 144′ is aligned withinsquares 134′. The alignment is to within a desired tolerance, t. In someembodiments, t is not more than 0.5 micron. In other embodiments, t maydiffer. Similarly, FIG. 10 depicts an alignment mark set in which arectangular alignment mark 144″ fits within a female alignment mark134″. Female alignment mark 134″ is shown as black, while male alignmentmark 144″ is shown as cross-hatched. One or more of the alignment marksets 134/144 depicted in FIGS. 5-8 may be replaced by the alignment markset 134′/144′, 134″/144″, or another alignment mark set. The alignmentis to within a desired tolerance, t. In some embodiments, t is not morethan 0.5 micron. In other embodiments, t may differ.

Similarly, other configurations are possible for the interlocking key148. FIGS. 11-17 are diagrams depicting exemplary embodiments of dotsforming an interlocking key for bonding substrates. For clarity FIGS.11-17 are not to scale and only a portion of the dots are shown. FIG. 11depicts an interlocking key 150 including dots 152 on one substrate anddots 154 on the other substrate. The dots 152 and 154 are placed suchthat the key locks the substrates to within a desired tolerance, t. FIG.12 depicts a key 150′ in which the dots 152′ and 154′ interlock to adistance that is less than the desired tolerance t. FIG. 13 depicts akey 150″ in which the dots 152″ and 154″ may form a bond, such as an Aubond. More specifically, the dots 152″ and 154″ actually come intophysical contact. FIG. 14 depicts a key 150′″ in which the dots 152′″and 154′″ are tapered. The taper may aid in guiding the dots 152′″ and154′″ to form the key 150′″ when the substrates are pressed together instep 104 of the method 100. Although all of the dots 152′″ and 154′″ areshown as being tapered, in some embodiments, only some of the dots 152′″and 154′″ might be tapered. For example, only the dots 152′″ might betapered, only the dots 154′″ might be tapered, or some portion of thedots 152′″ and some portion of the dots 154′″ might be tapered. In thekey 150′″, the dots 152′″ and 154′″ are in physical contact and may,therefore, form a bond. However, in other embodiments, the dots 152′″and 154′″ may be spaced apart. In addition, the dots 152′″ and 154′″ areshown as having a taper which ends in a flat surface. However, in otherembodiments, one or more of the dots 152′″ and 154′″ may taper to apoint. In addition, although shown as composed of flat surfaces, thetaper on the dots 152′″ and 154′″ could include curved surfaces. FIG. 15depicts a key 150″″ in which the taper on each of the dots 152″″ and154″″ is formed by a curved surface. In the key 150″″, the dots 152″″and 154″″ are shown in physical contact. However, in other embodiments,the dots 152″″ and 154″″ may be spaced apart.

FIGS. 16-18 depict keys in which the dots have various cross sections.For example, FIG. 16 depicts a key 160 in which the dots 162 and 164have circular cross sections. In the embodiment shown, the dots 162(which are white) may reside on one substrate while the black dots 164reside on another substrate. Thus, these dots 162 and 164 are analogousto those described above. FIG. 17 depicts a key 160′ in which the dots162′ and 164′ have a rectangular cross section. Thus the whiterectangles 162′ may reside on one substrate while the cross-hatchedrectangles 164′ reside on another substrate. FIG. 18 depicts a key 160″in which the dots 162″ and 164″ have a reentrant cross section. In theembodiment shown, the dots 162″ and 164″ have a cross shape. However,other reentrant shapes are possible. Thus the white crosses 162″ mayreside on one substrate while the black crosses 164″ reside on anothersubstrate. Thus, keys 160, 160′, 160″ having dots of variouscross-sections may be used. In addition, although depicted in aparticular configuration with a particular spacing between portions ofthe keys 160, 160′ and 160″, other spacings and/or configurations may beused. For example, any combination of the keys 150, 150′, 150″, 150′″,150″″, 160, 160′, 160″, and/or 148 might be used.

The keys 150, 150′, 150″, 150′″, 150″″, 160, 160′, and/or 160′ may beused in connection with the method 100. Thus, interlocking keys 150,150′, 150″, 150′″, 150′″, 160, 160′, 160″ of various configurations maybe used to retain the alignment through the reflow step. Thus, alignmentof the substrates may be improved. Consequently, bonding of substrates,for example for EAMR heads, may be improved.

1. A system for performing bonding of a first substrate to a secondsubstrate, the first substrate including a first plurality of solderpads, the second substrate including a second plurality of solder pads,the system comprising: a first alignment mark set and a first pluralityof dots on the first substrate, the first plurality of dots configuredto remain substantially solid during a reflow of the first plurality ofsolder pads; and a second alignment mark set and a second plurality ofdots on the second substrate, the second plurality of dots configured tointerlock and form an interlocking key with the first plurality of dots,the first alignment mark set being aligned with the second alignmentmark set corresponding to the first plurality of dots being aligned withthe second plurality of dots and the first plurality of solder padsbeing aligned with the second plurality of solder pads, the secondplurality of dots configured to remain substantially solid during thereflow.
 2. The system of claim 1 wherein the first plurality of dots andthe second plurality of dots include at least one of Au, Cu, Ni, andNiFe.
 3. The system of claim 1 wherein the each of the first pluralityof dots has at least one of a substantially circular cross-section, asubstantially rectangular cross-section, and a re-entrant cross-section.4. The system of claim 1 wherein the each of the second plurality ofdots has at least one of substantially circular cross-section, asubstantially rectangular cross-section, and a re-entrant cross-section.5. The system of claim 1 wherein the each of at least a portion of thefirst plurality of dots is tapered.
 6. The system of claim 1 wherein theeach of at least a portion of the second plurality of dots is tapered.7. The system of claim 1 wherein the first alignment mark set includesat least one male feature and the second alignment mark set includes atleast one female feature corresponding to the at least one male feature.8. The system of claim 7 wherein the first alignment mark set includes across pattern.
 9. The system of claim 1 wherein the interlocking key isconfigured to lock the first plurality of dots interlocks with thesecond plurality of dots such that the first substrate remains within adesired tolerance with respect to the second substrate during thereflow.